The present invention relates to mineral mining installations and more particularly to roof support assemblies usable in such installations.
In mine workings, and especially in coal mine workings, it is well known to provide a longwall scraper-chain conveyor which transports material detached from a mineral face by a machine, such as a plough, guided on the conveyor. Roof support assemblies are then arranged on the side of the conveyor remote from the mineral face. These assemblies are connected to the conveyor through shifting rams which serve, individually, to selectively advance the assembly or a portion of the conveyor up towards the face as the mineral winning progresses. Roof support assemblies are known in a variety of constructions and the present invention is concerned with assemblies of the type which employ a stowage or goaf shield lining which screens off the waste or fracture in the stowage zone caused by the partial collapse of the roof as the longwall moves up. In all forms of roof support assembly the actual support of the roof over the working is effected by one or more roof bars and it is desirable for these bars to extend right up to the face as far as possible. In certain known roof support assemblies which employ stowage shields the front end of the or each roof bar tends to move towards the face as the bar is lowered. Consequently, when the bar is set against the roof there must always be unsupported space between its front end and the roof part of the face to accommodate this movement. In order to overcome this problem it is known to provide a composite or multi-part screen and a compensating piston and cylinder unit which serves to bring the roof bar or bars towards the face when the bar or bars is being raised. An alternative construction has a multi-part roof bar which has an outer portion which can be moved towards and away from the face by means of a hydraulic piston and cylinder unit and locked in position. Both these constructions necessitate extra equipment and hence expense and can be disabledby jamming when waste material lodges in gaps.
It is also known to provide a system of guide or control rods which combine with a multi-part screen and ensure that the front end of the or each roof bar moves along a vertical line parallel to the mineral face. See for example Japanese patent publication 547032. This construction is better from the point of view of disablement but again extra expense is involved because of the special design. Moreover, an assembly of this type takes up considerable space in the mine working.
A general object of the present invention is to provide an improved form of support assembly.